This invention relates to optical imaging and more particularly to optical imaging utilizing a scanned light beam.
Scanned light beam imaging is employed for various purposes including electrophotographic printing, as in the IBM 6670 Information Distributor.
In such systems used for printing, a light beam generated, for example, by a laser is selectively modulated to vary its amplitude while it is scanned laterally across a moving photoconductor to selectively discharge the photoconductor. Such systems have been binary in nature ("on" or "off") to accomplish printing of character information by selectively either exposing the photoconductor or leaving it unexposed. To insure complete exposure, adjacent scan lines are usually overlapped slightly. Thus, any slight misalignment of the scans or change in beam size would not be noticed.
This cannot be done if the light beam modulation is other than binary because in any partial exposure, a substantial overlap would appear as a stripe of complete exposure. Alternatively, spacing the scans apart would appear as a stripe that remains unexposed. To attempt to prevent such stripes by substantially eliminating the optical and mechanical tolerances from the system would appear to be prohibitively expensive.
It is therefore an object of the present invention to eliminate the perception of elongated stripes in such optical imaging systems without requiring substantial tightening of allowable optical or mechanical tolerances.